The present invention relates to a contact type recording head which is relatively moved while its one portion being brought into contact with recording material (thermal transfer recording material, heat sensitive material, photosensitive heat sensitive transfer material, etc.) and which directly prints an image onto the recording material or indirectly prints an image onto an image receiving material through the recording material, and to an image forming apparatus using this contact type recording head.
For example, a thermal head, which is a contact type recording head, has heating elements arranged in an array-like manner in the direction of rotation axis of a platen, and forms an image onto the recording material by selecting and heating the heating elements corresponding to an image to be printed onto the recording material inserted between the platen and the heating elements. In this case, when the above-described recording material is a thermal transfer recording material (for example, ink ribbon), the ink of the ink ribbon is thermaly transferred onto the image receiving surface of the image receiving material as an image by the heating of the heating elements. When the recording material is heat sensitive material (heat sensitive paper) , an image is directly formed on the heat sensitive paper by the heating of the heating elements.
Incidentally, the conventional heating element is formed such that a convex glaze layer is formed on a ceramic substrate, and a resistance heating element, electrode layer, and protective layer are successively laminated thereon. Accordingly, the heating element contacts with the material through the protective layer. The protective layer is formed as the smooth one, and generally, the recording material is formed also as the smooth one by coating wax, or the like, on the contact surface with the head so as to reduce the frictional resistance.
However, in the contact type recording head which records an image by contacting with the recording material, the frictional resistance between the head and the recording material largely changes corresponding to the existence of the printing image, that is, an image-printing rate. Accordingly, in the case where the arrangement direction of a heating section is defined as the primary scanning direction, and the direction of the relative movement of the recording material with the head is defined as the subsidiary scanning direction, when an intermediate color printing area to continuously print the intermediate color in the subsidiary scanning direction, and a binary level printing area to alternately print white or black in the subsidiary scanning direction, are mixed, the frictional resistance between the recording material and the head changes due to a change of the image-printing rate in the binary level printing area, and a printing failure of so-called line-jumping which appears as a line-image in an intermediate color printing area, is generated. Further, in the contact type recording head using the recording material on which wax is coated, a fused amount of wax changes according to the image-printing rate, and thereby, the frictional resistance changes, resulting in a printing failure.
Further, when the head and the recording material are both formed with high smoothness, as described above, in addition to that the frictional resistance largely changes corresponding to the image-printing rate, a width of increase of the frictional resistance at that time tends to increase, and a large burden is loaded on component parts of a conveyance mechanism, which is a problem.
The present invention is attained in view of the foregoing situation, and the object of the present invention is to provide a contact type recording head by which a change of the frictional resistance due to the difference of the image-printing rate can be smaller, the image printing quality is increased, and a burden loaded on the component parts of the apparatus can be reduced, and an image forming apparatus using that head.
In order to attain the above object, a contact type recording head according to the present invention is structured as follows.
(1). A contact type recording head which moves relatively with respect to the recording material while its one portion being brought into contact with the recording material, and directly prints an image onto the recording material or indirectly prints an image onto an image receiving material through the recording material, the contact type recording head is characterized in that microscopic irregularity is provided on a material contact portion of the head with the recording material.
In the contact type recording head, the microscopic irregularity is provided on the material contact portion with the recording sheet, thereby, a change of the frictional resistance of the material contact portion with the recording material, which, conventionally, largely changes due to a change of the image-printing rate, is suppressed smaller, and a printing failure such as a line-jumping, or the like, hardly occurs. Further, when the difference of the change of the frictional resistance of the material contact portion with the recording material is made small, a change of the conveyance driving torque is smaller, and thereby, the durability of the component parts of the apparatus can be increased.
(2). A contact type recording head according to Item (1), wherein the microscopic irregularity is formed in a streak-like manner in the direction of the relative movement.
In this contact type recording head, the microscopic irregularity is formed in a streak-like manner in the direction of the relative movement to the recording material, therefore, the friction between the recording head and the recording material at the time of relative movement is not increased, and the contact surface of the recording head with the recording material is decreased. Further, when an abrasive sheet is inserted and passed through between the recording head and the recording material, the streak-like microscopic irregularity can be easily formed in the direction of the relative movement.
(3). A contact type recording head according to either one of Item (1) or Item (2), wherein the microscopic irregularity has an average roughness of 0.03-0.5 xcexcm in the direction perpendicular to the direction of the relative movement.
In this contact type recording head, the microscopic irregularity is formed such that the average roughness in the direction perpendicular to the direction of the relative movement is 0.03-0.5 xcexcm which is the appropriate roughness, therefore, the same printing failure as in the conventional head, caused by insufficient microscopic irregularity roughness, and reversely, uneven density caused when the microscopic irregularity is too rough, are both eliminated, thereby, good printing can be performed.
(4). A contact type recording head according to any one of Items (1)-(3), wherein a plurality of heating elements are arranged in the array-like manner on the material contact portion with the recording material.
This contact type recording head is used as so-called thermal head, in which heating elements are selected and heated, and thereby an image is thermally transferred. In this case also, a change of the frictional resistance between the material contact portion of the head and the recording material is reduced, and the printing failure due to a change of the image-printing rate hardly occurs. Further, because the contact area of the material contact portion is decreased, even if wax coated on the recording material is fused, a change of the frictional resistance can be suppressed to be smaller.
(5). An image forming apparatus is characterized in that the contact type recording head of any one of Items (1)-(4) is installed in the apparatus as a recording head.
In this image forming apparatus, the contact type recording head in which a change of the frictional resistance due to the difference of the image-printing rate is small, is installed, and therefore, generation of the printing failure such as line-jumping or the like, can be prevented, thereby, the printing quality can be increased.
(6). An image forming apparatus according to Item (5), wherein the average roughness of the surface of the recording material on which the recording head slides, is not more than 0.5 xcexcm.
In this contact type recording head, even if the recording material has high flatness in which the average roughness is not more than 0.5 xcexcm, it is coupled with the roughness of the head, and the frictional resistance becomes small and stable by the multiplication of the two, thereby, a change of the frictional resistance can be more effectively suppressed.
(7). An image forming apparatus according to either one of Items (5) or (6), wherein the recording material is thermal transfer recording material or heat sensitive material.
In this image forming apparatus, when the recording material is thermal transfer recording material, the head comes into contact with the thermal transfer recording material under the condition that a change of the frictional resistance is small, and by the heating of the head, an image is indirectly thermally transferred onto the image receiving surface of the recording material through the thermal transfer recording material. When the recording material is heat sensitive material, the head comes into contact with the heat sensitive material under the condition that a change of the frictional resistance is small, and by the heating of the head, an image is directly thermally transferred onto the heat sensitive material.
(8). An image forming apparatus according to either one of Items (5) or (6), wherein the recording material is heat sensitive transfer recording material which includes pigment of 30-70 weight parts and amorphous organic high polymer of 25-50 weight parts whose softening point is 40-150xc2x0 C., and has practically transparent heat sensitive ink layer whose film thickness is within the range of 0.2-1.0 xcexcm, and wherein the particle diameter of more than 70% of the pigment in the heat sensitive ink layer is not more than 1.0 xcexcm, and the optical reflection density of the transfer image is at least not less than 1.0 on the white base material.
In the image forming apparatus, when the recording material is heat sensitive transfer recording material of color material which is close to the practical printing ink, the texture or hue of the recording result can be equivalent to the print, thereby, the high quality image formation with excellent color reproducibility can be performed.